Spring finger ply downs are generally employed at each axial end of the drum of a tire building machine. Such assemblies generally comprise an annular array of generally axially extending spring fingers mounted to a support with their ply engaging ends projecting from the support toward the center of the drum and radially outwardly at an angle when in their unflexed condition. Such fingers are usually flexed radially inwardly by the axial movement of a bead setting device causing the ply engaging ends thereof to sweep or fold inwardly liner or ply material overhanging the ends of the drum. In this manner the materials of the tire are turned down over the shoulder or edge of the drum to form a shoulder of tire material rigidly backed by the edge or shoulder of the drum for receipt of the tire bead. Thereafter with the bead setter and ply down retracted axially away from the drum, the ply material will normally be turned and stitched around the bead and up over the top of the drum by a dual bladder assembly such as seen, for example, in Cannurati U.S. Pat. No. 3,438,832 or in Enders U.S. Pat. No. 4,302,274.
A problem associated with early spring finger ply downs was that they were difficult to assemble. Also, replacement of a damaged or bent finger in such ply down assemblies was a difficult and tedious task. The problem is similar to trying to assemble a barrel without special tools or jigs, or trying to replace a single barrel stave without affecting adjacent barrel staves. In such ply down assemblies, the fingers usually were clamped between two rings which had to be separated for assembly of the fingers or removal of a single finger. Consequently, assembly of the fingers or replacement of a single finger was difficult to accomplish without affecting or loosening adjacent fingers.
One approach to the problem is disclosed in U.S. Pat. No. 4,238,268. In tnis patent the spring fingers are mounted between inner and outer rings that are secured together by a plurality of mounting screws. At least one ring is formed of an elastomer and each finger has a radially inwardly bent toe which hooks over the inner ring. When a finger is to be removed, the mounting screws nearest the finger on each side thereof are removed so that the elastomeric ring can then be bent or distorted radially away from the finger a distance sufficient to free its toe thereby to permit withdrawal of the finger. A replacement finger then may be inserted in reverse manner. Although it may be possible to carry out this operation without freeing adjacent fingers, replacement of a single finger would still be somewhat tedious requiring several mounting screws to be removed and then secured back into place. Obviously, replacement of several fingers would present a more tedious project as would the initial assembly of the ply down. Also, a rather large number of mounting screws are needed. Moreover, the inner ring located interiorly of the fingers must be large enough in radial thickness to accommodate the mounting screws and this may preclude the use of long length turn-up bladders because of inadequate interior clearance.
In Yuhas U.S. Pat. No. 4,353,771, there is disclosed a finger ply down assembly which affords greater facility of the assembly and/or replacement of the spring fingers. The fingers are secured between two nested rings which are constructed to interfit with each other and with each finger so that each finger may be inserted or removed by simply flexing the finger to clear a projection on one of the rings which interfits with the finger in its normal position. With such assembly, a finger may be inserted or removed without disturbing adjacent fingers and without disassembly of the nested rings even at an area approximate the finger to be inserted or removed. Also, one of the rings may be made of a locally deformable material to permit each finger to be bent to clear the interfitting projection thereby to assist in the insertion and removal of the finger.